1. Technical Field
The present invention relates to a test apparatus and a measurement apparatus. Particularly, the present invention relates to a test apparatus and a measurement apparatus for measuring an electric current consumed by a device under test (load).
2. Related Art
A test apparatus has a function of measuring an average current to be consumed by a device under test when the device operates. The test apparatus detects a current output from a power source device that supplies a drive voltage to the device under test, and measures the average current consumed by the device under test.
Here, the power source device is slow in responding to any change in the current consumed by the load. Accordingly, the test apparatus has a bypass capacitor having relatively large capacitance, between its power source line and the ground, in order to compensate for any response delay of the current output from the power source device. With this, the test apparatus can supply a drive current to the device under test even in a case where it makes the device under test operate in such a manner as would require the current consumed by the device under test to change quickly.
Here, in a case where the test apparatus has a bypass capacitor, the current to be consumed by the device under test and the current output from the power source device do not coincide. Hence, the test apparatus cannot correctly measure the average current consumed by the device under test, by detecting the output current from the power source device.
Thus, a conceivable test apparatus to overcome this problem is such one that has, near the device under test, an AD converter which samples the drive current to be supplied to the device under test. However, since the drive current supplied to the device under test changes quickly, the test apparatus has to make the AD converter perform sampling quickly. Accordingly, the test apparatus has to be provided with a high-performance AD converter. Further, since there will be a large amount of data that should be taken in, the test apparatus has to be provided with a data memory having a large capacity.
Furthermore, in testing multiple devices under test of about several hundreds or so simultaneously, the test apparatus has to have the same number of current measuring sections as the number of devices under test. Therefore, it is preferred that the test apparatus be structured as a simple circuit in order to be able to measure the average current consumed by the device under test.
When measuring the current of the device under test, a measurement error is caused by an offset in the operating amplifier used by the measuring circuit. To solve this problem, it is necessary to adjust the offset to be equal to zero. But if a plurality of measurement channels are provided, it is necessary to adjust the offset of each channel because each operating amplifier has a different offset. To achieve this, a way to adjust the error caused by the offset automatically and with the same process is sought.
During the initial evaluation of the device under test, the value of the value of the current may be sought in addition to the test result indicating pass/fail of the current test of the device under test. Therefore, a way to easily obtain the current value is desired.